IMPROVEMENTS IN OR RELATING TO COMMUNICATION SYSTEMS

AMELIORATIONS RELATIVES A DES SYSTEMES DE COMMUNICATIONS

English Abstract

A communication system for the mutual interconnection of a plurality of lower
traffic level (5 Terabit) switch nodes via a relatively higher traffic level
(Petabit) connection bus, which system comprises in operative association with
each node, a two part TDM optical data management interface, wherein a first
of the two parts comprises a time slot resequencer which serves to provide for
the transmission of data from its associated node to the bus, and wherein a
second of the two parts comprises a time slot specific combiner which serves
for the transmission of data from the bus to its associated node, each node
and the bus having independent data scheduling.

French Abstract

L'invention concerne un système de communications destiné à l'interconnexion entre une pluralité de noeuds de commutation à faible charge de trafic (5 térabit) via un bus de connexion à charge de trafic relativement élevée (pétabit). Ce système comprend une association fonctionnelle à chaque noeud, ainsi qu'une interface de gestion de données optiques TDM en deux parties. La première partie comprend un séquenceur d'intervalles de temps qui permet de transmettre les données entre son noeud associé et le bus. La seconde partie comprend un mélangeur spécifique d'intervalles de temps qui permet de transmettre les données entre le bus et son noeud associé, chacun des noeuds et le bus présentant une programmation de données indépendante.

Claims

CLAIMS:
1. A time division multiplexing (TDM) optical communication system for mutual
interconnection of a plurality of switch nodes via a connection bus comprising
in operative
association with each node, a two part TDM data management interface, wherein:
a first of the two parts comprises a time slot resequencer which serves to
provide
for the transmission of data from its associated node to the bus, wherein the
timeslot
resequencer of each interface comprises an optical splitter fed from its
associated switch
node and coupled to the bus via a timeslot selector, a time delay device, and
an optical
combiner which feeds the bus, and wherein
a second of the two parts comprises a time slot specific combiner which serves
for
the transmission of data from the bus to its associated node, wherein the
timeslot-specific
combiner of each interface comprises a time delay device, a timeslot selector
and an
optical combiner via which its associated switch node is fed from the bus,
each node and
the bus having independent data scheduling, the switch nodes being operational
at a lower
traffic transmission level than the connection bus, the data being transmitted
optically
between the switch nodes, the interface, and the bus.

2. A communication system as claimed in claim 1, wherein the switch nodes of
the
system each comprise ingress ports coupled to the timeslot resequencer of an
associated
interface, and egress ports coupled via grating means and a time slot selector
to the time
slot-specific combiner of this associated interface.

3. A communication system as claimed in claim 1 or 2, wherein the interface is

arranged to provide for 5 Terabit coupling between the switch nodes and the
bus, and for
Petabit coupling between the bus and the switch nodes.

4. A communication system as claimed in any one of claims 1 to 3, wherein the
switch nodes each comprise a 128X128 switch fabric.

Description

CA 02439783 2006-05-24

1
IMPROVEMENTS IN OR RELATING TO COMMUNICATION SYSTEMS.
FIELD OF INVENTION
The present invention relates to communication systems. More particularly but
not
exclusively it relates to such systems which use optical TDM (time division
multiplex)
switch cores.

BACKGROUND OF THE INVENTION

TDM switch cores are well known to the cognoscenti and moreover, the operation
of an optical backplane and/or apparatus for use therewith is described, for
example, in
Great Britain Patent Application Nos. GB 2353157A, and GB 2362280A.
Accordingly,
neither detailed switchcore description nor detailed optical backplane
description herein, is
believed to be necessary.

The capacity of the apparatus described in GB2362280A is limited by the
throughput of the optical backplane. Typically this is 5 Terabit/s. However in
the future,
higher capacity switch cores will be required and these can be achieved by the
interconnection of a plurality of 5 Terabit/s switch nodes so that any one or
more of the
ingress ports of any one of such nodes can be selectively connected to the
egress port or

ports of any other of such nodes via a static Petabit/s optical connection
bus. Therefore, it
is desirable to provide an optical interconnection system to satisfy this
particular
requirement. It should however be understood, that the present invention may
also find
more general application in communication systems.

SUMMARY OF THE INVENTION

In a first aspect of the invention, there is provided a time division
multiplexing
(TDM) optical communication system for mutual interconnection of a plurality
of switch
nodes via a connection bus comprising in operative association with each node,
a two part


CA 02439783 2006-05-24

2
time division multiplexing TDM data management interface, wherein: a first of
the two
parts comprises a time slot resequencer which serves to provide for the
transmission of
data from its associated node to the bus, wherein the timeslot resequencer of
each interface
comprises an optical splitter fed from its associated switch node and coupled
to the bus via

a timeslot selector, a time delay device, and an optical combiner which feeds
the bus, and
wherein a second of the two parts comprises a time slot specific combiner
which serves for
the transmission of data from the bus to its associated node, wherein the
timeslot-specific
combiner of each interface comprises a time delay device, a timeslot selector
and an
optical combiner via which its associated switch node is fed from the bus,
each node and

the bus having independent data scheduling, the switch nodes being operational
at a lower
traffic transmission level than the connection bus, the data being transmitted
optically
between the switch nodes, the interface, and the bus.

Other aspects and features of the present invention will become apparent to
those
ordinarily skilled in the art upon review of the following description of a
specific

embodiment of the invention in conjunction with the accompanying figures.
BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the present invention will now be described, by way of
example
only, with reference to the attached figure.

Fig. 1 is a schematic representation of an embodiment of a switch node
interconnection system of the present invention.

DETAILED DESCRIPTION

Referring now to the drawing, a communication system comprises a plurality of
5
Terabit switch nodes, only two of which 1, and 2, are shown in the drawing for
simplicity
of description. Each of the nodes 1, 2, comprises a 128X128 single node switch
fabric.


CA 02439783 2006-05-24

2a
The node 1, includes ingress ports 3, coupled to an output line 4, and egress
ports 5, each
coupled to an input line 6, via a timeslot selector 7, and an optical grating
8, switch
operation being locally controlled by means of a scheduler 9. The other node
2, is
substantially identical comprising, ingress ports 10, coupled to an output
line 11, and

egress ports 12, each coupled to an input line 13, via a time slot selector
14, and an optical
grating 15, switch operation being locally controlled by a scheduler 16.

In order to connect any one or more of the ingress ports 3, of the node 1, via
an
optical bus arrangement which may be implemented as a crossconnect 17, which
has its
own scheduling engine 18, to any egress port of any other node, (such as one
of the egress

port or ports 12, of the node 2, for example), a two level traffic management
interface
system is provided which comprises for each node a similar Petabit expansion
box. In this
particular embodiment boxes 19, and 20, for the nodes 1, and 2, respectively
are provided.


CA 02439783 2003-08-29
WO 02/076138 PCT/GB02/01295
3
The expansion box 19, handles traffic to/from the node 1, and comprises a
time slot resequencer 21, which operates on the 5 Terabit level to couple the
ingress
ports 3, to the crossconnect 17, and a time-slot specific combiner 22, which
operates
on the Petabit level to couple the crossconnect 17, to the egress ports 5.
Similarly, the expansion box 20, handles traffic to/from the node 2, and
comprises a time slot resequencer 23, which operates on the 5 Terabit level to
couple
the ingress ports 10, to the crossconnect 17, and a time-slot specific
combiner 24,
which operates to on the Petabit level to couple the crossconnect 17, to the
egress
ports 12.
The time slot resequencer 21, operating on the 5 Terabit level, comprises an
optical splitter 25, fed from the line 4, a time slot selector 26, a time
delay 27, and an
optical combiner 28, coupled to the crossconnect 17, whereas its associated
timeslot-
specific combiner 22, which operates on the Petabit level, comprises time
delay 29,
fed from the crossconnect 17, timeslot selector 30, and an optical combiner
31, which
is coupled to the line 6, so as in effect to reverse the data expansion
process.
Similarly, the time slot resequencer 23, which operates on the 5 Terabit
level,
comprises an optical splitter 32, fed from the line 11, a time slot selector
33, a time
delay 34, and an optical combiner 35, coupled to the crossconnect 17, whereas
its
associated timeslot-specific combiner 24, which operates on the Petabit level,
comprises time delay 36, fed from the crossconnect 17, a timeslot selector 37,
and an
optical combiner 38, which is coupled to the line 13.
It will be appreciated that although only two nodes are shown in this example,
several nodes may be similarly interconnected to the crossconnect 17, each via
its
own Petabit expansion box.
In operation, the system as just before described utilises algorithms which
run
at two levels, i.e. the 5 Terabit level of the switch nodes and the Petabit
level of the
extension system comprising the expansion boxes 19, and 20, and the
crossconnect
17, each node being responsible for managing the slot allocation or scheduling
of its
own backplane. It will pass to the extension system, information concerning
traffic
destined for other nodes with which it is linked via the extension system.
Once the
extension system has opened a connection between two nodes, the local node
will
select which of its ingress ports will transmit to the egress port of the
external node
and pass that information to the traffic management system of the external
node.


CA 02439783 2003-08-29
WO 02/076138 PCT/GB02/01295
4
In order to carry information on the ingress nodes backplane, it must be
extracted from that backplane, moved in time and inserted into a new slot on
an
extension backplane. This will carry the traffic to the external node where it
will again
be extracted, moved in time and inserted into the appropriate slot of the
egress nodes
back plane. This is in effect an optical time and space switch which is
defined in this
system by the splitters, couplers and delay lines/devices as shown.
A system as just before described has the advantage that use of the timeslot
resequencers facilitate independent delay for each of the 128 timeslots and
moreover,
all 128 could be outputted if so required. In operation, the timeslot-specific
combiners
provide a 128:1 optical switch with 50 Pic/sec switching speed. It will be
appreciated
that scheduling resolves internal/external time slot contention and that the
implementation is inherently scalable in accordance with traffic requirements.

Representative Drawing